1. Field of the Invention
This invention relates to an automatic apparatus and method for detecting arterially-induced pulsations and automatically determining the pulse rate, and systolic and diastolic blood pressure.
2. Description of the Prior Art
It is known in the prior art that arterially-induced pressure pulsations may be detected by means of an electrostatic microphone responding to the pressure pulsations in a compressing fluid as disclosed in Bouche U.S. Pat. No. 2,851,030. Further, the use of microphones and electrostatic pressure conversion elements are disclosed in Luisada U.S. Pat. No. 2,297,905 and Speaker, et al U.S. Pat. No. 2,452,799. Further, Zuidena U.S. Pat. No. 2,989,051 uses pulsation pressure information along with cuff pressure information to derive blood pressure reading. Utilizing this same approach in most recent art is shown in the following references: German Pat. No. 3,008,601; Nakayama U.S. Pat. No. 3,920,004; Link et al U.S. Pat. No. 4,009,709; Link et al U.S. Pat. No. 4,074,711; Wohltjen et al U.S. Pat. No. 4,078,551; Gangirard et al U.S. Pat. No. 4,177,801; Danna et al U.S. Pat. No. 4,261,368; Jewett U.S. Pat. No. 4,290,434; Ramsey III U.S. Pat. No. 4,349,034; Ramsey III U.S. Pat. No. 4,360,029; Jewett U.S. Pat. No. 4,417,586; Nunn et al U.S. Pat. No. 4,427,013.
The need to measure both the systolic and diastolic blood pressure and the pulse rate utilizing an automatic procedure was required.
A unique method for not only determining the pulse rate but determining the systolic and diastolic blood pressure was discovered.
It was further discovered that upon inflating the bladders in the instant invention that the pressure within the bladder would impend upon the pressure transducer. More specifically, the pressure inside the bladder impends upon a diaphragm located in the pressure transducer, preventing the diaphragm from responding to arterially-induced pressure pulsations in the bladder. The inflation pressure which is much greater than the arterially-induced pressure pulsations in the bladder, interferes or prevents the diaphragm from reacting or flexing in response to these arterially-induced pulsations. It was discovered that a pressure equalization passageway was necessary in order to equalize the pressure between the interior of the bladder and the interior of the pressure transducer chamber. This passageway allows equalization of pressure on both sides of the pressure transducer diaphragm. The size of the passageway is critical since it must be of a sufficient size to allow pressure equalization between the inflation pressure in the bladder and the interior of the pressure transducer chamber and not interfere with the pressure transducer diaphragm reacting to or sensing the arterially-induced pulsations generated in the bladder. Further, it was discovered that pressure transducers have different sensitivities to arterially-induced pulsation amplitudes. Consequently a device was discovered for use in conjunction with the instant sensor for decreasing the amplitude of the arterially-induced pulsation amplitudes such that pressure transducers of varying sensitivity may be used.
The prior art disclosed many methods for determining blood pressure and pulse rate, three of the most pertinent prior art references are the following: Croslin U.S. Pat. No. 4,271,844; Croslin U.S. Pat. No. 4,326,537 and Croslin U.S. Pat. No. 4,407,297. These are all related companion patents.
In the above mentioned patents, each is comparing the detective sequence of the relative amplitudes of a predetermined number of blood pressure pulses with a plurality of known valid sequences to determine if the detected sequences are valid. In the instant invention, the above known valid sequences, is not a fixed number derived from data. Further, in the above patents, if the detected sequence is determined to be valid, then the systolic pressure is determined to be the registered occluding pressure at the onset of a predetermined blood pressure pulse. This determination of the occluding pressure in the instant invention is determined at a different point of reference. Further, as set forth in these references, in determining the diastolic pressure, to be the registered occluding pressure at the onset of a pre-selected pulse, in a predetermined number of last pulses when the representative value is less than the threshold value, this does not disclose the instant method. Further, and most imporantly, these patents are concerned with the detection of the Korotkoff sound whereas the instant invention is concerned with detecting arterially-induced pressure pulsations as distinguished from audio sound detection. Further, in the above patents, these methods are registering the value of a sample which is generated at the start of a blood pressure pulse and maintained for the duration of at least several, but not all, of the succeeding blood pressure pulses. In the instant invention, all the arterially-induced pulsations and pressures are stored and used to compute blood pressure values and pulse rate after the cycle has been completed. In the above patents, these methods are merely taking a window from the data and using the figures from this window to determine blood pressure. The methods disclosed in the above patents are discarding all the other readings outside this window area. Further, these patents are deriving the "height" of a blood pressure pulse by substracting the respective value registered in their step (c) from the larger sample value of the respective blood pressure pulse and maintaining such height for the duration of at least several, if not all, of succeeding blood pressure pulses and then taking slight variations on that one sensor signal. In the instant method, there are separate sensors used in determining the occluding and diastolic pressure and the systolic pressure.
As to U.S. Pat. No. 3,978,848 which discloses a blood pressure and rate monitor wherein the inflatable cuff contains a pressure responsive transducer that performs two functions. The first function is providing a first signal corresponding to the gauge pressure in the cuff and the second function provides a second signal corresponding to variation in the cuff pressure produced by expansion and contraction of the occluding artery due to the pumping action of the heart.
U.S. Pat. No. 3,905,354 claims a method of automatically measuring the patient's systolic and diastolic blood pressure by several steps including generating quantized pressure signals in response to pressure pulses to provide individually defined pressure signals of a uniform amplitude.
In both U.S. Pat. No. 3,978,848 and U.S. Pat. No. 3,905,354 neither disclose apparatuses or methods for aleviating the problem of the bladder inflation pressure impending upon the pressure transducer thereby preventing the pressure transducer from detecting arterially-induced pulsations and generating electrical signals having amplitudes corresponding to the pulsations. Further, the above prior art discloses no apparatus or method for adjusting the sensitivity of pressure transducers to the amplitudes of these pulsations. Further, the above prior art does not disclose or suggest the instant method.